A voltage regulator is an essential part of a vehicle charging system, for keeping a lead acid battery in a charged condition and also to supply the energy requirements of the vehicle when the engine is running. Typically when the engine is at stand still the lead acid battery connected to the electrical circuit of a two wheeler supplies the electrical demands. Older versions of two wheelers where invariably of “kick start” type, requiring a manual and forced rotation of the crank shaft to induce engine start. This rotation also energized a direct current generator or magneto (A small dynamo with a secondary winding that produces a high voltage) enabling a spark to jump between the poles of a spark plug in a gasoline engine. The modern two wheelers invariably have a “self start” system having a starter motor for starting the vehicle. Also modern two wheelers use an alternator having permanent magnet rotors, to produce alternating current, as it is more rugged and maintenance free as compared to a generator producing direct current.
The voltage regulator includes a feed back and control circuitry for varying output voltage of the alternator in accordance to the load changes of the vehicle's electrical components such as lights, signal system, horns and engine control systems. The load conditions vary considerably in twilight mode and night mode. The voltage regulator also includes a power rectification circuit connected to the feedback and control circuitry. The feedback and control circuitry changes the duty cycle of the generator or alternator by increasing or decreasing the power output of the rectification circuit in a predetermined manner based on monitored load changes. The feedback and control circuitry comprises of integrated semiconductor device which has circuits adapted to sense continuously variable physical quantity and magnitudes in discrete units of a physical quantity. These circuits can be configured by programming the integrated semiconductor device.
A battery charging systems consist broadly of the following components:                1) Three phase regulator systems        2) AC voltage regulators/DC voltage regulators        3) Shunt (short) type/Open (series) type regulators        4) SCR based/MOSFET based/IGBT based power rectification systems.        
A suitable combination of the above components is selected, to meet the needs of battery charging and energizing system. Depending on the electrical design of the vehicle two or more of the above components are used in an automotive battery charging system for motorcycles. The output of the power rectification circuit is controlled in accordance to the load changes of the vehicle's electrical components by the feedback and control circuitry for meeting the instantaneous electrical loads in either alternating or direct current modes and also apply a constant voltage difference across the terminals of the lead acid battery in direct current mode.
Typically two wheeler regulator rectifiers are designed to rectify the alternating current output of the alternator into a DC voltage of 14.5 volts and feed the regulated voltage to the battery whenever the voltage across the battery terminals fall below the designated voltage.
U.S. Pat. No. 4,659,977 discloses a microprocessor-based electronic voltage regulation system for controlling the charging of the battery in a vehicle. The conventional voltage regulator is eliminated and the microprocessor of the engine control unit (ECU) is used to regulate the output of the alternator. The battery temperature signal from a temperature transducer and a battery voltage signal from a sense line connected directly to the positive terminal of the battery are supplied to the microprocessor through an analog-to-digital converter. The temperature signals are used to select a desired set point voltage for charging the battery based on relationship between battery temperature and desired battery voltage with preset maximum and minimum voltage set point levels. Excitation current supplied to the rotor windings is controlled in accordance with a comparison between the desired set point voltage and the battery voltage signal by a control signal generated by the microprocessor using a power switching circuit. Other input to the ECU includes vehicle deceleration, throttle position, and engine RPM and elapsed time since ignition. These inputs are further processed to modify the desired voltage set point or modify engine RPM in accordance with driving conditions. Over-current protection for the logic circuitry and improved diagnostic capabilities are also provided.
This type of system for battery charging using a microprocessor is not a stand-alone system and is dedicated for specific application and will have to custom designed and built for different vehicles. Also it will necessarily involve many discrete circuits and components, making the unit very expensive. Any failure of a component of the system will affect the overall performance. In such a system fault tracing will be time consuming and will have to carried out by trained and skilled personnel.
Thus, there is a need for a device that is adapted to carry out battery charging operation in an automotive two wheeler application which overcomes the problems hitherto encountered in the prior art devices.